1. Field of the Invention
The present invention relates generally to medical apparatus and more particularly to an improved orthopedic pin and clamp for an external fixator.
2. Description of the Related Art
The ILIZAROV (TM) external fixator provides for the anatomical reduction of bone injuries requiring high stability of the bone fracture segments, and preservation of injured limb functions and early mobilization. For example, the ILIZAROV external fixator is typically used for open and closed fracture fixation pseudoarthroses of long bones (both congenital and acquired), limb lengthening by epiphyseal or metaphyseal distraction, correction of bone or soft tissue deformities, and correction of bone or soft tissue defects. The external fixator uses essentially a bloodless surgery technique, allows for the treatment of patients with complex diseases and bone defects that would otherwise have been unsuccessfully treated with traditional methods.
The main parts of the ILIZAROV external fixator are the standard elements used to correct skeletal deformities. These standard elements include wires, full rings, half rings, arches, wire fixation bolts, detachable wire fixation buckles and dual sided wire fixation buckles. Generally, the wires are fixed to the full rings and half rings of the wire fixation bolts at each of their ends after being passed through an osteal bore and the soft tissue in the limb of a patient.
The secondary parts of the fixator are necessary for the assemblage of the apparatus, namely threaded rods, telescopic rods, threaded rods with slots, connection plates, curve and twisted plates, supports and posts, hinges, washers, sockets, bushings, bolts and nuts. To assemble the numerous pieces of equipment, various types of wrenches and wire pinchers are needed. Additionally, various general orthopedic instruments are required such as chisels, hammers, pinchers and power drills to insert the wires. An exemplary assemblage of the external fixator is described in greater detail hereinbelow with reference to FIG. 9. A more detailed description of the external fixator is found in the Ilizarov et al., U.S. Pat. No. 4,615,338 for an Automatic Compression Distraction Apparatus.
Generally, the many elements of the external fixator provides great flexibility in use of the apparatus. For example, the wires may be inserted in many different directions at different levels of the effective limb, or adjustment of the rings permit reassembly or adjustment of the apparatus during the course of patient treatment. The proper position and orientation of bony segments are maintained to achieve continuous reduction. Also, the correction of the direction and type of forces that act on the bone during the course of treatment are allowed. Finally, the necessary degree of stability to allow early weight bearing and reduce complications during the course of treatment is obtained.
The wires can be introduced into the bone and fixed to the main and secondary supports of the fixator. A mechanical action of slow and gradual compression or distraction of bony segments is possible in many different directions. It is also possible to combine multiple treatment levels through the action of different wire placements. Fine precision movement as well as large forces of distraction are possible. During the course of patient treatment, the loads acting on the bone through the wires will have maximum stability and can be used to correct bony problems.
There are many advantages to the external fixator. Because the pins are small in diameter, the blood and nerve supplies including the intramedullary canal are not severely compromised. A further advantage is the minimization of further trauma to the anatomy and the gradual movement of the bony segments during the treatment process. Because of the tensioning effects of the pins, the bone is continuously loaded unlike a plate or any other type of internal fixation. The bony loading seen in the axial direction is one of a natural and uniformed nature. The blood supply is not compromised, and the bone is loaded by known biological laws of the natural frequency of magnitude. The tension wires are remarkably resistance and have enough elasticity so as to allow a proper biological stimulus to bone healing.
To allow the bony segments to be moved during the courses of treatment, some of the wires used in the external fixator include a stopper thereon as best seen in prior art FIGS. 1 and 2. The stopper abuts against the bone and allows the wires to be angulated in a variety of ways and positioned at any point along the fixation rings. By paying attention to vascular and nerve anatomy, the pins can be placed through the bone at different levels and angles. The bony segment to be moved under the tensioning of the wire.
In the prior art, the stopper is formed on selected ones of the pins by dropping a piece of solder thereon. The disadvantage and limitation of the use of the solder is that the heat dissipated by the molten solder onto the steel pin destroys the heat tempering of the pin. Since the solder abuts against the bone at the osteal bore, the disruption of the heat treatment may cause the pin to break at the solder. Furthermore, the solder itself may break off from the pin causing the bone to shift position on the pin negating the benefits of the treatment.
Another disadvantage and limitation of the above device is that when the pins are clamped to the rings, sheer forces are developed in the pin at the interface of the head of a bolt which clamps the pin down or at the edge of the ring itself. The sheer forces may cause the pins to break at this location.